Federal agents say about 90 percent of the 12,000 pistols and rifles the Mexican authorities recovered from drug dealers last year and asked to be traced came from dealers in the United States, most of them in Texas and Arizona. . . .

Those who support the assault weapons ban as a way to curb violence cite figures from the Bureau of Alcohol, Tobacco, Firearms and Explosives that say American gun sellers supply the Mexican drug cartels with 95 percent to 100 percent of their guns. . . .